AC Joint Separation on MRI & X-ray: Imaging Findings

AC separations are classified by ligament injury and clavicle displacement. Type I is an AC ligament sprain; type II adds AC ligament rupture and CC ligament injury; type III disrupts both. Types IV, V, and VI describe posterior, marked superior, and inferior displacement. Examination and X-rays assess alignment; type I can look normal on X-rays.

Types I and II AC separations are treated conservatively with sling immobilization, ice, analgesics, and progressive physical therapy, with excellent functional outcomes. Type III injuries are the most controversial — the majority of patients treated nonoperatively return to full function, while surgery is reserved for high-demand overhead athletes, manual laborers, and those with persistent symptomatic instability after 3 months of conservative management. Types IV, V, and VI — with posterior, markedly superior (>100% CC distance), or inferior-subcoracoid displacement respectively — are treated with surgical stabilization. Surgical techniques include hook plate fixation, coracoclavicular ligament reconstruction with synthetic or autograft tissue, and AC joint stabilization with suture button devices. Concurrent rotator cuff or labral tears identified on MRI are addressed arthroscopically at the same time.

The majority of patients with type I and II AC separations recover fully within 6–12 weeks with conservative management. Type III injuries treated nonoperatively achieve satisfactory outcomes in 80–90% of patients, although persistent AC joint prominence and mild functional deficits are common. Chronic AC joint pain from post-traumatic osteoarthritis of the AC joint can develop years after any grade of separation, presenting as pain with cross-body adduction and overhead activities. Distal clavicle resection, performed arthroscopically, reliably alleviates chronic AC joint arthritis pain. High-grade injuries treated with surgical stabilization have good return-to-sport rates, though hardware complications, loss of reduction, and coracoclavicular ossification are recognized risks.